this fixes the problem Axel signaled with the OK button in terminal's about box

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@14922 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/servers/app/Layer.cpp

@@ -1481,9 +1481,7 @@ Layer::_ReserveRegions(BRegion &reg)
 void
 Layer::_ClearVisibleRegions()
 {
-	// OPT: maybe we should uncomment these lines for performance
-	//if (fFullVisible.CountRects() <= 0)
-	//	return;
+	fDrawingRegion.MakeEmpty();
 
 	fVisible.MakeEmpty();
 	fFullVisible.MakeEmpty();